1. Field of the Invention
The present invention concerns storage-stable, liquid carbodiimide-modified polyisocyanates having isocyanate contents of approximately 20 to 45 percent by weight based on the total weight and a process for their manufacture.
2. Description of the Prior Art
The manufacture of carbodiimide-modified polycondensation products is known according to the data in German Pat. No. 1,130,594. Organic, low molecular compounds containing at least two isocyanate groups are condensed in the presence of 0.01 to 10 percent by weight, based on the weight of the polyisocyanate, of phospholines or phospholidines or their oxides, as catalysts, at temperatures ranging from room temperature to 300.degree. C. The carbodiimide-modified polycondensation products have average molecular weights of at least 750 and may be used for the manufacture of molded materials, fibers, films and foils.
According to German Published Application No. 2 245 634, adducts consisting of phospholine oxides, phospholine sulfides, phospholane oxides or phospholane sulfides with monoalcohols, dialcohols and/or polyalcohols of molecular weights from 32 to 250, protic acids, metal salts or acid chlorides are described as catalysts for the manufacture of foams containing carbodiimide groups.
Due to their high activity, these catalysts are very well suited for the manufacture of foam and resins containing carbodiimide groups but not for the manufacture of polyisocyanates containing carbodiimide groups.
According to data in German Patent Application No. 1,668,083, polyisocyanates possessing carbodiimide-isocyanate adducts are prepared by heating organic polyisocyanates in the presence of 0.01 to 10 mole percent based on organic compounds of a biuret, urea, amide, urethane, allophonate, isocyanurate, uretidione or uretonimine as catalysts to above 150.degree. C. and cooling the resulting reaction products to room temperature.
Storage-stable, liquid isocyanate adducts based on 4,4'-diphenylmethane diisocyanates are also produced in accordance with German Patent Application No. 1,593,619 by heating said diisocyanate to temperatures of 160.degree. to 250.degree. C. in the presence of 0.1 to 3 percent by weight of a trialkyl phosphate, trialkenyl phosphate, triaralkyl phosphate, triaryl phosphate, tricycloalkyl phosphate or tricycloalkenyl phosphate. The drawback of this process is that the condensation must be carried out in the presence of relatively large amounts of catalyst at temperatures above 150.degree. C. resulting in numerous by-products, for example, isocyanurate by-products, which are formed in addition to the desired adducts possessing carbodiimide groups. These condensation products have low storage stability since the reaction is stopped merely by cooling the reaction mixture. Thus, the condensation continues at room temperature albeit at a slower rate.
Further disadvantages are that the carbodiimide adducts are relatively dark due to the high reaction temperatures and that suspended therein are variable amounts of solids as by-products which must be removed at additional processing costs.
In order to avoid these drawbacks, processes are described in German Published Application Nos. 2,537,685; 2,606,419 and 2,614,323, wherein condensation occurs in the presence of phospholines, phospholidines and/or their oxides at temperatures below 200.degree. C. and is terminated by adding hydrogen halides, sulfur and phosphorus halide compounds, organic acid halides, Lewis acids, alkyl sulfates and toluenesulfonic acid esters, metal-II and metal-III halides, and silica-based adsorbents.
Using these procedures, it is possible to produce room temperature stable carbodiimide-modified polyisocyanates. The disadvantage of this process, however, is that the phospholine oxide salts and/or adducts formed during the terminating process act as carbodiimide-producing catalysts for isocyanates so that the polycondensation is renewed at slightly increased temperatures and/or must be removed by employing, among others, such solid absorbing substrates as animal charcoal, diatomaceous earth, Fuller's earth, and zeolite.
The purpose of this invention, therefore, was to produce stable, liquid, nearly colorless carbodiimide-modified polyisocyanates under relatively mild reaction conditions which do not exhibit the above-described disadvantages.